Name_________________________________
ALE #4 Mitosis & Meiosis
Control of Cell Division and Cancer
22. Define the functions for each of the following.
a.) Proto-oncogenes – These are genes that code for growth factors (growth factors
are protein messengers that stimulate cell division). When mutated, these genes
become oncogenes (cancer-causing genes).
b.) Oncogenes – These arise from mutated proto-oncogenes. An oncogene causes
cancer by unregulated production of growth factors. (In other words, they produce
way too much gowth factor!)
c.) Tumor suppresser genes - In their normal state these genes code for proteins that
turn off mitosis (i.e. prevent cell division). When mutated these genes cause cancer
(unregulated cell division)
d.) p53 gene – A tumor suppressor gene that holds the cell cycle in the G1 phase.
When mutated, this gene causes cancer (unregulated cell division).
23. Why doesn’t one mutant Tumor Suppresser Gene (e.g. one mutant p53 gene) cause
cancer? We need multiple mutations in several cell-cycle genes to cause cancer
24. a.) What kind of gene is the BRCA 1 gene?
It is also a tumor-supressor gene
b.) Why do women that inherit a mutant BRCA 1 gene have a very high chance (8090% chance) of getting breast cancer? This is because these women have
inherited a mutant (recessive) form of the gene from either Mom or dad. They
only need to acquire a mutation in the other allele (on the other homologue) to get
a mutant BRCA1 gene.
c.) Why are the percentages much lower for the average woman?
Because most women inherit the non-mutated (dominant) form of the gene. Thus they
need the genes on BOTH homologues to mutate in order to get cancer.
25. List three different factors that can cause genes (e.g. p53 gene, BRCA 1 gene, etc.) to
mutate
a.)viruses
b.)toxins
c.)radiation
26. Phase-specific Chemotherapies. Indicate how each of the following methods of
controlling the growth of cancerous cells can be accomplished.
a.) How could you prevent the cells from entering mitosis?
–Block growth factor receptors on cell membrane with antibody (e.g. Herceptin)
b.) Once started, how can you stop the chromosomes from completing mitosis?
Taxol: interferes with the movement of the chromosomes along spindle fibers
c.) How could you block the S phase? –Methotrexate and other chemotherapeutic drugs
block DNA synthesis
27. What is cancer? •Cancer is a genetically dictated loss of cell cycle control
28. How are cancerous cells different from normal cells?
1.Immortal - will not stop dividing
2.Altered cell membranes means they can’t anchor & so they metastasize: spread into
other tissues
3.Have lost the genetic ability to stop dividing
4.Cancer is heritable: Cancer cells give rise to cancer cells
5.Are dedifferentiated - less specialized than the cell it came from
6.No contact inhibition
7.If not treated will eventually cause death
29. How do you get cancer? i.e. What genes need to mutate for normal cells to become
cancerous cells? The most common way that people get cancer is by a mutations in
tumor-supressor genes like p53 or by mutations in proto-oncogenes
Meiosis
1. a. What is the function of meiosis?
to produce gametes, cells with half the number of chromosomes as their parent cells.
Gametes function in sexual reporduction
b. What kinds of cells are produced by meiosis?_____sex cells
(gametes)________________________________________
c. Are these cells haploid or diploid?
___________________________________haploid___________________
d. What would be the genetic consequences to a species (i.e. to the number of
chromosomes) if mitosis, rather than meiosis, produced these cells?
The gametes would each have a diploid number of chromosomes, and so when the
gametes fuse the zygote would be tetraploid. All animal zygotes would die in this
situation (but not plants – they can have multiple ploidies).
2. Overview of Meiosis…
a. How do the chromosomes align at metaphase I of meiosis?
with their homologous pairs
b. What separates during anaphase I of meiosis?
homologous pairs
c. How do the chromosomes align at metaphase II of meiosis?
individually, randomly
d. What separates during anaphase II of meiosis?
sister chromatids
e. How do the daughter cells compare genetically? all four are genetically different
f. Are the daughter cells haploid or diploid?haploid
Meiosis—Apply your knowledge!
30. The following questions refer to the sketch below that represents the nucleus of a skin
cell from a hypothetical species of worm.
a.) In figure 1, above, use a pencil or pen to shade in the maternal chromosomes. Leave
the paternal chromosomes as they are (white). Notice that there are 8 duplicated
chromosomes in the figure above. They make four homologous pairs. One of each
homologous pair should be shaded. I have drawn in arrows to show which four
chromosomes should be shaded. The other four could have been shaded in instead.
b.) Draw the chromosomes of a cell from the species of worm in figure 1 in each of the
following stages of cell division—mitosis or meiosis. Be sure you have the correct
number of chromosomes in each of your diagrams. Use the maternal/paternal colors
you used in part a, above.
Use the figures in Campbell to check your drawings
(i.) Skin cell in metaphase of mitosis
This cell should have 8 chromosomes, and each
chromosome should be duplicated (2 sister
chromatids). All 8 should be lined up individually
at the equator of the cell. Four of the 8 should be
shaded. The 8 chromosomes can be aligned in any
particular order.
(ii.) Skin cell in anaphase of mitosis
This cell should look exactly the same as (i),
but just after the sister chromatids (of each
chromosome) split and begin to move to
opposite poles of the cell.
(iii.) Pregamete cell in metaphase I of meiosis
This cell should have 8 chromosomes, and each
chromosome should be replicated (2 sister
chromatids). All 8 should be lined up IN PAIRS at
the equator of the cell. In other words, there
should be 4 sets of homologous pairs at the
equator. One chromosome of each pair should be
shaded The 4 pairs can be aligned in any
particular order, and any arrangement of
maternal/paternal chromosomes
(iv.) Pregamete cell in anaphase I of meiosis
This cell should look exactly the same as (iii),
but just after the homologous pairs separate.
Thus four replicated chromosomes should be
headed toward one pole, and four should be
headed towards the other pole. One
chromosome of each pair should be shaded
(v.)
(vi.)
The two cells at end of meiosis I. Are
these cells haploid or diploid? ____haploid_________ How can you tell?
They each have 4 chromosomes (replicated)
instead of 8. One chromosome of from
each original pair should be shaded
The four cells at the end of meiosis II.
Are these cells haploid or diploid? ______haploid________ How can you
tell? They each have 4 chromosomes
(unreplicated) instead of 8. Follow
through with the shading patterns from
the previous box.
31. a. Explain why the age of the mother and not that of the father is correlated with the
probability of having a child with Down syndrome.
Because mom’s pre-egg cells are arrested in metaphase I until ovulation. In metaphase I,
the chromosome are attached to the spindle fibers. Spindle fibers degenerate with age,
leading to nondisjunction.
b. Explain how nondisjunction of chromosomes during anaphase I of meiosis can lead to
Down syndrome. The homologous pair #21 is misaligned at Metaphase I. Thus the
homologues don’t separate at Anaphase I, and one cell gets both homologues and the
other cell gets none. Thus one of the gametes has two copies of chromosome 21. When
this gamete is fertilized, the zygote now has three copies of chromosome 21.
c. Starting with a cell with four chromosomes (i.e. 2n = 4) in metaphase I of meiosis,
show how an error in anaphase I can lead to a situation that could lead to Down
syndrome See Fig 8.21 in text
Nondisjunction at Anaphase I
n+1
n+1
n-1
Metaphase I
Anaphase I
n-1
Metaphase II
Anaphase II
Gametes
32. Explain how each of the following leads to genetic variation during meiosis.
a. Independent assortment of chromosomes during metaphase I of meiosis
See Fig 8.17 Homologous chromosomes line up in metaphase one with their homologous
pairs, but they have a random alignment. Thus maternal and paternal chromosome get
shuffled when they assort into the daughter cells during meiosis
b.
Cross over during prophase I of meiosis Paternal and maternal chromosomes of
each homologous pair from a tight tetrad during prophase I of meiosis. While in
this tetrad, they may exchange sections of DNA, creating chromosomes that are
genetically different from BOTH parents. See Fig 8.18 in text.
7. Compare mitosis and meiosis by completing the table below.
Mitosis
somatic
Meiosis
sex cells
1
2
2
4
same
different
diploid
haploid
no
yes
cell division in body cells
(tissue repair, hair
growth…)
production of gametes (egg
& sperm) for sexual
reporduction
Type of cells involved
Number of cell divisions involved
Number of daughter cells
How do the daughter cells compare
genetically?
Are the daughter cells diploid (2n) or
haploid (n)?
Involves homologue pairing and cross
over?
Role played in organism